1. Field of the Invention
This invention relates in general to surface treatment of metals, and particularly to those for steels requiring wear resistance under heavy loads, such as those imposed upon earth boring drill bit bearings.
2. Description of the Prior Art
Various treatments are known in the prior art for the surfaces of metals, such as steel, which are used to provide hard, wear resistant surfaces upon the metals so treated. One prior art treatment technique is carburization.
The bearing surfaces of rotatable cutters in earth boring drill bits are commonly carburized, hardened and tempered to increase their wear resistance. Gas carburizing is a known technique which has been used in the past to produce a uniform case on the head section bearings of earth boring drill bits. Although gas carburizing provides good process control and a uniform resulting case, it can be a time consuming and expensive operation when a selectively applied case is required as on rock bit parts. Methods of selectively carburizing require masking of some areas with a coating to prevent carburization. Methods such as copper plating or using case preventive paints are used as masks for selective carburizing, but add cost to the processing.
Pack carburizing is another technique utilized in the manufacture of earth boring drill bits. A particulate carburizing compound is packed in a container which surrounds the drill bit bearing area which is to be treated. Selective carburization is accomplished by only surrounding the area needed with carburizing compound. The container and section of the bit head being treated are then placed into a furnace and heated at a temperature and for time sufficient to allow carburization.
One problem in obtaining a uniform case in pack carburizing is caused by low carbon potential furnace gases leaking into the container which surrounds the bearing area and holds the carburizing compound. Another problem which can result in poor carburization is shifting of the container and resulting loss of the compound due to handling or vibration in the furnace.
In order to prevent the infiltration of furnace gases into the carburizing container and movement of the container and loss of compound, Applicants tried various fixtures in an attempt to create a seal or affix the container to the bit head. These attempts included the use of wires which were fixed in the interior of the container and which radiated inward from the container internal diameter. Fixturing washers or rings were also used in an attempt to secure the container about the bit head. Each of these attempted solutions possessed certain disadvantages which made the attempted technique less than satisfactory.